VIC is a pencil and paper cypher using a straddling checkerboard as well as several other known techniques used to further obfuscate the message.

To encrypt, a straddling checkerboard is set-up by following the rules:

- The first row is numbered from to .
- The second row is populated with the most frequent letters of the alphabet (
`ESTORNIA-R`

), in no particular order, and by leaving two blanks below two arbitrary numbers from the first row. - The remaining rows are numbered with the numbers from the first row that have a blank in the second row.
- The remaining rows are then filled-in with the rest of the alphabet (in no particular order).
- Any spare cells which can be filled with any non-literal character.
- It does not matter where the spaces and the non-literal characters are placed as long as the receiver uses the same system.

0 1 2 3 4 5 6 7 8 9 --------------------- E T A O N R I S --------------------- 4 B C / D F G H J K L --------------------- 6 M P Q U V W X Y Z .

To encrypt, every letter from the checkerboard is mapped to rows and columns (or just columns if it occurs in the second row).

As an example, to encrypt `let there be`

:

L E T T H E R E B E 49 0 1 1 46 0 7 0 40 0

The resulting message `4901146070400`

can be sent out directly or processed further through a second cypher stage such as transposition or substitution. As an example, we can add a key 0727 using modular arithmetic:

4901146070400 0727072707270 ------------- (+) 4628118777670

Optionally, the same straddling checkerboard can be used to convert the cypher-text back into letters. Since we have chosen two blanks for `4`

and `6`

, whenever we find those numbers in the first position, we group the numbers together (because `4`

and `6`

have a blank space in the second row of the checkerboard and cannot be converted to letters):

46 2 8 1 1 8 7 7 7 67 0 ----------------------- H A I T T I R R R Y E

resulting in the cypher-text: `HAITTIRRRYE`

.

In order to decrypt, one must know the chosen structure of the checkerboard and the successive operations used to obtain the cypher-text.

In essence, VIC is a hybrid cypher that combines multiple methods of substitution and transposition in order to obtain the cypher-text. It is a very strong cypher due to the number of operations performed during encryption but that also results in a larger shared secret between the sender and the receiver - ie: the checkerboard structure is arbitrary, the whole thing must be established before messages can be sent; adding a key to the procedure for a further transposition also means that the key must be known and, lastly, the order of operations must be known in order to be able to reverse the cypher.

fuss/csharp/cryptography/cyphers/vic.txt ยท Last modified: 2017/02/22 18:30 (external edit)

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